Horizontal-axis propeller, ducted venturi, kite principle, flexible-foil VAWT, oscillating hydrofoil
Every underwater turbine we build descends from one of five architectures. Each has a different sweet spot in current velocity, cost, and mechanical complexity. The Axial Labs swarm combines them: the right architecture at the right site, tied together by the same monitoring and control protocol.
Cp = 0.45. The underwater wind turbine. Three blades, horizontal shaft, aligned with current. This is what MeyGen, Verdant, Orbital, and ANDRITZ deploy at MW scale. The physics is identical to wind turbines. Betz limit applies (theoretical max Cp = 0.593). Real-world marine propeller turbines hit 0.40 to 0.48.
Our AXL-T series of tubular propeller turbines for in-pipe deployment is already this architecture, miniaturized for pipes. Scaling from 300 mm pipe diameter to a 2 m open-water rotor is parametric. Same blade element momentum theory, same NACA profiles, same OpenFOAM simulation pipeline. The design toolchain carries over with no redesign.
| Component | Cost |
|---|---|
| 2 m CNC aluminum rotor (3 blade) | $5,000 to $8,000 |
| Direct-drive PMA generator, underwater-sealed | $3,000 to $5,000 |
| Structural frame and gravity base | $5,000 to $10,000 |
| Total per unit | $15,000 to $25,000 |
Output: 20 to 50 kW in a 2 to 3 m/s current.
Cp = 0.55 to 0.60. Take the horizontal-axis propeller. Put a converging-diverging duct (a venturi) around it. The duct accelerates the water before it hits the blades and creates a low-pressure zone behind the turbine that pulls more water through. Published research consistently shows a 30 to 50% power increase over bare rotors at the same blade diameter.
Why this is our best ocean option. The duct is a shaped pipe section, and we already manufacture shaped pipe sections for in-pipe turbines. The fabrication skills transfer directly. A duct for a 2 m rotor is a fiberglass or sheet-metal cone. Local marine composites shops build boat hulls with more complex geometry every day.
| Current | Bare rotor (Cp 0.45) | Ducted rotor (Cp 0.55) | Uplift |
|---|---|---|---|
| 2 m/s | 7.4 kW | 9.0 kW | +22% |
| 3 m/s | 24.9 kW | 30.5 kW | +22% |
The duct adds roughly $2,000 in fabrication cost and about $5,000 per year in additional revenue per unit. Payback in five months.
Dozens of published papers with full duct geometries, angles, contraction ratios. The optimal duct profile (NACA 4412 or a similar cambered section revolved around the axis) is textbook aerodynamics applied to water. Research from Oxford, TU Delft, and INSEAN provides complete parametric design guidelines. No patents gate the concept. Ducted turbines predate patent law.
Entry cost: bare-propeller cost + $2,000 to $3,000 for the duct. Total $17,000 to $28,000 per unit.
Minesto proved the physics. A device flying through water in figure-eight patterns experiences velocity five to ten times higher than the ambient current. Power scales with velocity cubed, so this means 125 to 1,000 times more energy density per unit of swept area compared to a stationary turbine. A small turbine on a fast-moving kite extracts more energy than a large stationary turbine in the same current.
The principle is not patentable. It is Bernoulli and Newton. Lift on a hydrofoil, tether constraint creating figure-eight motion, velocity multiplication through dynamic flight. The specific Minesto wing shape and control algorithm are their implementation. The underlying physics belongs to everyone.
Kite at 8 m/s effective velocity (1.5 m/s ambient)
0.5 m ducted propeller, Cp = 0.50
rho = 1025 kg/m^3 (seawater)
P = 0.5 * Cp * rho * A * v^3
P = 0.5 * 0.50 * 1025 * 0.196 * 512
P ~ 25,754 W ~ 26 kW
Same 0.5 m rotor, stationary, same current:
P ~ 0.27 kW
The kite multiplied output by 96 times.Not because Minesto invented it. Because Bernoulli described it 300 years ago and almost nobody has applied it underwater until recently.
A hydrofoil wing (NACA 63-series or similar high-lift section) with a small ducted propeller turbine mounted on it, tethered to a seabed anchor, with an autopilot board (open-source ArduPilot or PX4 adapted for underwater) controlling the flight path via control surfaces on the wing. The wing does not need to be 12 m like the Dragon 12. A 3 to 4 m wingspan kite is enough.
Entry cost per unit: $14,000 to $25,000 for 20 to 30 kW output. Comparable cost to a stationary turbine, 10 to 50 times more power per unit in the same current.
Cp = 0.37, but self-starting. A vertical-axis turbine with flexible composite blades that passively adjust their camber as they rotate. Instead of rigid NACA profiles (Gorlov, Darrieus), the blades bend and twist like a fish tail, optimizing the angle of attack at every rotational position. A spring-loaded pivot at the blade root allows passive pitch adjustment.
Why it matters. Self-starts in currents as low as 0.3 m/s. No external power to spin up. No pitch mechanism, no control system, no electronics required for basic operation. The simplest possible ocean turbine. Drop it in the water and it starts spinning.
Deploy twenty of these at $3,000 to $5,000 each across potential tidal sites. Each self-starts, generates 1 to 5 kW depending on current, and reports flow velocity and power data back to CommandCC via a simple cellular IoT module. You have just mapped every viable tidal energy site in the Salish Sea for $60,000 to $100,000, without a single environmental assessment, because at this scale the units are classified as monitoring equipment, not power generation infrastructure.
Once you know which sites have the best currents (confirmed by six months of real data from your scout nodes), you deploy the ducted propellers or kites at the proven sites. The scouts become permanent power sources for the monitoring equipment at each site.
Entry cost per unit: $3,000 to $5,000 for 1 to 5 kW.
No rotating parts. A hydrofoil oscillates up and down in the current like a whale flipper. The pitching and heaving motion drives a linear generator or hydraulic pump. Zero rotating machinery. Zero bearings in water. Zero seals to fail. The simplest mechanics possible for ocean energy.
Why it is interesting. The failure mode that kills most ocean turbines is bearing failure and seal failure from saltwater corrosion and biofouling on rotating shafts. Oscillating hydrofoils eliminate this entirely. The power takeoff can live above the waterline (hydraulic lines run up to a surface float) or integrated as a linear generator in the pivot mechanism.
Stingray (Engineering Business, Scotland) published complete test results. Multiple university groups have published full CFD and experimental datasets. The concept is older than most patents. Oscillating foil propulsion was studied by the military in the 1970s.
Entry cost per unit: $7,000 to $13,000 for 5 to 15 kW.
